This invention relates to improvements in the electrodeposition of copper from aqueous acid copper plating baths, and preferably from aqueous acid copper plating baths containing one or more bath-soluble copper salts, free acid and chloride ions.
Acid copper plating baths for producing a brilliant copper finish on articles have been known in the art and a number of patents have described various brightening agents which can be added to the acidic baths. Examples of such patents include U.S. Pat. Nos. 2,707,166; 2,707,167, 2,830,014; 3,276,979 and 3,288,690. Brightening agents comprising organic sulfonic and carboxylic acids, or their salts, have been suggested. In U.S. Pat. No. 3,725,220, it has been suggested that the utilization of organic sulfonates or carboxylates as brightening additives in acidic aqueous copper plating baths results in improved stability of the bath and effective deposition of copper over a satisfactory current density range.
In a number of instances in the prior art acid copper plating baths, a sufficiently brilliant finish is obtained but little or no smoothing effect on the surface is obtained. The ability of a plating bath to produce deposits relatively thicker in small recesses and relatively thinner on small protrusions thereby decreasing the depth of surface irregularities is known as "leveling". For example, a copper plating bath with satisfactory leveling ability can be utilized to reduce or eliminate the effect of microscopic cracks or scratches on the surfaces of the articles being plated. Additives for increasing the leveling effect of acid copper plating baths have been developed and described in the art. For example, U.S. Pat. No. 3,101,305 describes a leveling additive obtained from the condensation of thiourea with aliphatic aldehydes such as, for example, formaldehyde. Such derivatives reportedly provide a greater smoothing or leveling effect than the previously known and described thiourea derivatives. The use of certain heterocyclic sulfur-nitrogen organic compounds such as derivatives of 2-thiazolidinethiones or reaction products of such sulfur-nitrogen compounds with alkyl dialdehydes to provide smooth bright electroplates from copper baths is described in U.S. Pat. No. 3,798,138.